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Past Issues

Plant and Insect Diagnostic Clinic Update - August 27, 2008

This article was published originally on 8/27/2008

The following are a few of the problems received the past two weeks.

Diseases and Disorders

The clinic has been receiving tree samples that are positive for oak wilt. Oak wilt is a fungal disease that enters the vascular system of the oak tree and causes characteristic leaf symptoms and eventually the death of the tree. Please see our Oak Wilt pamphlet for symptoms of oak wilt and most importantly how to submit a sample for testing.

The other wilt we have been receiving is pine wilt. Pine wilt is caused by a nematode that is carried by a wood boring beetle. Once in a susceptible tree the nematodes rapidly reproduce and plug up the vascular system. In Iowa, scotch pine is very susceptible, and it is rare other pines. Needles brown rapidly and the tree often dies within a few months of symptoms first appearing. There is no cure for pine wilt once a tree begins showing symptoms. We test for the nematode in the lab and if it is present it is important for the homeowner to completely remove and chipper the tree to prevent spread to other Scotch Pines. Please see our pamphlet for information on how to test for pine wilt.

And since we are talking wilts, I might as well mention Verticillium wilt. Verticillium wilt, like oak wilt, is a fungal disease. Verticillium wilt affects many different tree species, including oak. Verticillium is a soil borne fungus, and it is important not to replant another susceptible tree species in a spot where a tree died from verticillium wilt. For information on symptoms, how to test for the disease, and susceptible and resistant tree species please see our pamphlet, Verticillium Wilt of Woody Plants.

Insects

Soldier beetles are appearing again on flowers. These distinctive beetles attract a great deal of attention as they buzz on flowers in the warm sun, feeding on pollen. Some references call these beneficial, predatory insects the leatherwings. They are closely related to lightningbugs and they are ecologically beneficial. No control is needed. See our web site or BugGuide for more information.

Wheel bugs are noticed in the fall of the year, more commonly in the southern half of the state. See the photo below. The wheel bug is a member of the assassin bug family. These predators feed on other insects and are considered beneficial. Wheel bugs may bite if handled.

The imperial moth is moderately common but very sporadic in Iowa, with more specimens this summer than usual. The caterpillars (photo below) feed on the foliage of many different trees (basswood, birch, cedar, elm, hickory, Honeylocust, maple, oak, pine) but the numbers are usually too few to make a difference and they are not considered to be a pest of Iowa's trees. Control is not required. The moth stage will not appear until next Spring and will be a large yellow moth marked with purplish-brown spots.

Soldier beetles are common on goldenrod and other flowers in the fall. Photo by Laura Jesse.

Wheel bug. Photo by Neric Smith.

Imperial moth caterpillar. These caterpillars are highly variable in color.